Primary total knee arthroplasty, in which the natural femoral and tibial condylar bearing surfaces are replaced for the first time with prosthetic femoral and tibial components, has been practiced for many years with a high rate of success using a variety of different designs for the primary femoral and tibial components. It is usually preferred, if possible, to preserve the lateral and medial collateral ligaments during primary total knee arthroplasty and implant non-linked femoral and tibial components in order to preserve the stability and freedom of motion of the repaired joint. Examples of non-linked primary components highly suitable for use in cases in which the surgeon is able to preserve functioning lateral and medial collateral ligaments are disclosed in U.S. Pat. Nos. 3,728,742; 4,081,866; 4,209,861 and in the copending, commonly assigned U.S. patent application Ser. No. 350,130, filed Feb. 18, 1982, entitled "Bone Prosthesis with Porous Coating", now U.S. Pat. No. 4,550,448. In a rare number of cases, usually associated with improper surgical alignment of the primary components or the development after primary arthroplasty of severe conditions of arthritis or infection at the knee joint, it may become necessary to replace the originally implanted primary prosthetic components with a set of replacement femoral and tibial components, i.e. to practice revision total knee arthroplasty.
Revision total knee arthroplasty necessarily involves the removal of additional bone tissue (beyond the bone tissue removed for the primary arthroplasty) from the distal end of the femur (including the posterior region thereof) and the proximal end of the tibia in the preparation of those bones for implantation of the revision components. Prior to the present invention, the usual practice in cases in which the collateral ligaments are preserved has been to implant a primary type of femoral component having a spaced pair of bearing members as the revision component and to restore the full natural length of the patient's leg in extension by utilizing an appropriately-dimensioned revision tibial component having a spaced pair of bearing members that are much thicker than those of the replaced primary tibial component. The effect of this prior art practice is to shift the transverse joint plane, the horizontal plane passing through the lateral and medial component contact areas, in a proximal direction with respect to the normal anatomical transverse joint plane and to displace the femoral component anteriorly with respect to the natural anatomical distal femur. The prosthetic knee joint is stable in extension but unstable in high flexion, e.g. 90.degree. flexion, because of the unnatural shortening of the collateral ligament length in high flexion resulting from the uncompensated bone removal in the posterior region of the distal femur effected in preparation for implantation of the revision femoral component.